Many polypeptide pharmaceutical compositions are utilized for the treatment of diseases in humans and other mammals. Due to their high lability following oral delivery, polypeptide drugs must generally be delivered by parenteral routes. Chief among these routes are subcutaneous, intramuscular and intravenous.
Polypeptide drug products are traditionally supplied to pharmacies, hospitals and patients as solutions, suspensions, or lyophilized products. In liquid form, each polypeptide drug formulation requires a certain minimum level of chemical and physical stability for a defined length of time governed by treatment regimen, patient convenience, patient safety and regulatory guidelines.
To avoid pain or possible tissue damage, liquid polypeptide drug compositions are designed to provide tonicity or osmolarity close to that of the bodily fluids at or surrounding the site of administration. Excipients such as glycerin, dextrose, mannitol, lactose and salts such as sodium chloride are often used for this purpose. Examples of polypeptide drug products employing glycerin as an isotonicity agent include those comprising as active agent human insulin, insulin lispro, insulin aspart and glucagon.
Glycerin has also been used in pharmaceutical compositions as a solubilizer, wetting agent, emulsifier, solvent, bulking substance, antioxidant, chelating agent and preservative [Spiegel, A. J., et al., J. Pharm. Sci. 52:917–927 (1963); Wang, Y-C. J, et al., J. Parenteral Drug Assoc. 34:452–462 (1980); Remington's Pharmaceutical Sciences, Mack Publishing Company 18th Edition, p. 1316 (1990); Li, S., et al., J. Pharm. Sci. 85:868–872 (1996); Sieger, G. M., et al., U.S. Pat. No. 4,016,273, issued 5 Apr. 1977; Heinz, D. N., WIPO publication WO98/29131, 9 Jul. 1998].
For some polypeptide formulations, physical instability precludes the use of salts for isotonicity, a problem often solved by employing glycerin. Glycerin, however, is known to contribute to chemical instability in polypeptide products. In particular, impurities present in glycerin, such as aldehydes, are believed to initiate covalent crosslinking reactions leading to polypeptide dimers and polymers. See, for example, Bello, J., et al. [Arch. Biochem. Biophys. 172:608–610 (1976)]. For insulin products, such dimers and polymers have been linked to antigenicity and cutaneous allergy as described in Robbins, D. C., et al. [Diabetes 36:838–841 (1987)]; Robbins, D. C., et al. [Diabetes 36:147–151 (1987)]; and Ratner, R. E., et al. [Diabetes 39:728–732 (1990)]. Brange, J., et al. [Pharm. Res. 9:727–734 (1992)] concluded that covalent insulin dimers and polymers should be minimized to avoid these allergic reactions but no methods to achieve this goal were disclosed or suggested.
Three observations may be made about the problem of preparing reliably stable polypeptide compositions containing glycerin for parenteral administration. First, there has been a lack of a simple but accurate assay for determining the level of reactive aldehydes present in glycerin that lead to crosslinked polypeptide impurities. Second, there has been no teaching or suggestion in the prior art that commercial lots of glycerin manufactured from different sources should be evaluated to determine if certain sources are better than others in minimizing the polypeptide crosslinking reactions. Third, there has been no convenient, efficient way of lowering the reactive aldehyde content of glycerin to eliminate or minimize the aldehyde-induced crosslinking reactions in aqueous, pharmaceutical polypeptide compositions. Each of these three observations will now be described in more detail.